1. Technical Field
The present invention relates to performance optimization of an optical sub-system and, more particularly to utilizing an embedded digital processor to provide the optimization.
2. Description of the Prior Art
In most optical communication systems, various sub-system arrangements (for example, transmitters, receivers, transceivers, amplifiers, regenerators) exhibit variations in performance as a function of ambient temperature, device aging, power supply fluctuations, input signal levels, etc. (referred to categorically hereinafter as "environmental" changes). Analog feedback circuitry is often utilized to provide a moderate degree of control in some situations as, for example, controlling the bias current applied to a laser in a transmitter, the transimpedance gain of a receiver pre-amplifier, the gain of an optical amplifier, or various combinations of the above.
It has been recognized that such a discrete, analog circuit approach to the problem of sub-system stability results in increasing the size, cost, and complexity of the associated sub-system arrangement. Additionally, each analog circuit must, in most cases, be individually tuned to optimize the performance of the associated sub-system, further increasing manufacturing time and cost.
U.S. Pat. No. 4,924,191 issued to L. A. Erb et al. on May 8, 1990 discusses a solution to the various problems associated with utilizing analog feedback circuits (in this case, however, not for an optical system, but an electrical power amplifier). As disclosed, the operating bias point for an electrical power amplifier is stored in a computer memory. During frequent test intervals (when an incoming signal is interrupted), a test signal is passed through the power amplifier and a test bias point is measured. The test bias is then compared (by the computer) with the operating bias stored in memory. If they differ, the memory is updated to load the test bias value and the operation mode of the amplifier is re-started, where the updated value will be used to bias the amplifier until the next test period is initiated. The computer, alternatively, may be programmed by the user to bypass the test mode and continuously run using a user-supplied bias voltage value.
One problem with the arrangement as disclosed by Erb etal. is that the electrical power amplifier must be frequently removed from service and tested to obtain up-dated operating parameters. For most optical communication system arrangements, such an interruption in performance is unacceptable. Thus, a need remains in the art for a means of optimizing the performance of optical communication arrangements in light of various environmental changes which avoids the various drawbacks associated with analog feedback circuitry solutions.